Montelukast (trade name Singulair) is a leukotriene receptor antagonist (LTRA) used for the maintenance treatment of asthma and to relieve symptoms of seasonal allergies.[2][3] Montelukast comes as a tablet, a chewable tablet, flash tablet and granules to take by mouth.[4] Montelukast is usually taken once a day with or without food.[4] Montelukast is a CysLT1antagonist; it blocks the action of leukotriene D4 (and secondary ligands LTC4 and LTE4) on the cysteinyl leukotriene receptor CysLT1 in the lungs and bronchial tubes by binding to it. This reduces the bronchoconstriction otherwise caused by the leukotriene and results in less inflammation.

Because of its mechanism of action, it is not useful in the treatment of acute asthma attacks.

Side effects include gastrointestinal disturbances, headaches, and hypersensitivity reactions, in addition to other generic adverse reactions. Eosinophilia has also been documented as well as edema in post-marketing. There is no exact statement connecting the two events in the FDA label information, however it is known that the drug Valproic acid which has an adverse effect of eosinophilia is directly linked with lymphadenopathy which is known to lead to edema.

In March 2008, the U.S. Food and Drug Administration (FDA) announced that it would investigate whether mood changes and suicidal thoughts are possible side effects of drugs in this class, including the popular drug Singulair, which currently lists these side effects.[9]

Montelukast, unlike many drugs, has very few drug-drug interactions. This is due to the lack of off-target affinity towards other targets in the body where it might exert an effect. However, it is important to note that montelukast is an inhibitor of the drug metabolizing enzyme CYP2C8. Therefore, it is theoretically possible that the combination of montelukast with a CYP2C8 substrate (e.g. amodiaquine, an anti-malarial drug) could increase the plasma concentrations of the substrate.[11][12]

Schering-Plough and Merck sought permission to market a combined tablet with loratadine (Claritin) and montelukast (Singulair), as many patients combine the two themselves. However, the FDA has found no benefit from a combined pill for seasonal allergies over taking the two drugs in combination,[13] and on April 25, 2008, issued a "not approvable" letter for the combination.[14]

Ludwig Aigner from Paracelsus Medical University in Austria presented findings at the October 2015 meeting of the Society for Neuroscience in Chicago which showed that administration of Montelukast to older rats rejuvenated their brains, returning the same functionality as that of young rats. Human trials are planned, starting with Parkinsons patients.[15] The researchers conducted the experiment with montelukast because it reduces inflammation in the lungs and they thought it might also reduce inflammation in the brain. Some research has suggested that decline in memory skills may be associated with inflammation in the brain.[16]

Singulair was covered by U.S. Patent No. 5,565,473[17] which expired on August 3, 2012.[18] The same day, the FDA approved several generic versions of montelukast.[19]

The United States Patent and Trademark Office launched a reexamination of the patent covering Singulair on May 28, 2009. The decision was driven by the discovery of references that were not included in the original patent application process. The references were submitted through Article One Partners, an online research community focused on finding literature relating to existing patents. The references included a scientific article produced by a Merck employee on the active ingredient in Singulair. A previously filed patent had been submitted in the same technology area.[20] Seven months later the U.S. Patent and Trademark Office determined that the patent in question was valid based on the initial reexamination and new information provided, submitting their decision on December 17, 2009.[21]

Montelukast is sold under a variety of brand names including Montair-10,Montelo-10, Monteflo, and Tukast L in India, Montril, Lumona, Lumenta, and Arokast in Bangladesh, Monkast in Nepal, Respicare in Pakistan, Montelair in Brazil and AirOn in Venezuela .